The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

SA welfare group wants tax changes

South Australia's peak welfare body will urge the state government to revamp the tax system to make it simpler and fairer.

The South Australian Council of Social Service (SACOSS) will tell a state parliamentary committee on Thursday that current tax revenue is too low and the tax base too narrow.

"Our state tax system is sick and we have to address this if we want to have a healthy funding base for all the services that our community needs, the schools, hospitals, police and support for vulnerable members of our community," SACOSS executive director Ross Womersley said in a statement.

"It is not providing the money to fund our essential services and infrastructure and it is not always efficient or fair."

SACOSS will ask the government to consider replacing stamp duty on the purchase of a home with a broad-based land tax and introduce an unused building tax on property not serving the public benefit.